1. Field of the Invention
The present invention relates in general to automatic lapping machines, and in particular to automatic lapping machines which feed one or more streams of parts onto and off of a lapping table without human intervention.
2. Description of Related Art
Traditional lapping machines have a large horizontally-arranged, generally circular table provided with multiple, pie-shaped lapping stone sections arranged around a common central vertical axis. A suitably sized electric motor provides the motive power to rotate the table through a conventional clutch-brake and gear reducer combination. The lapping table may include two, three or four heavy conditioning rings equiangularly spaced around the table. The lower annular slotted surface of each conditioning ring rubs against the table and serves to help keep the surface of the lapping stones very flat. A supply of conventional lapping compound and cleansing lubricant is continuously pumped onto the table by a recirculating pump system to help carry away metal lapped off the parts being processed and any disintegrated lapping stone. This fluid is filtered to remove the fine metal particles and debris suspended in the fluid, and then is recirculated. The conditioning rings themselves are held in place by conventional roller retainer wheels supported by a simple superstructure suspended above or to the side of the table. Mechanical or fluid-power means such as a hydraulic cylinder may be provided for raising or lowering one or more of the conditioning rings relative to the lapping surface of the table. The retainer wheels preferably include ball or roller bearings, and may be strategically placed about the inner circumference of the conditioning ring so that the conditioning ring can readily rotate about its own axis as the table rotates beneath it. This rotation of the conditioning rings is induced by the frictional forces caused by the rotation of the table.
On a conventional lapping machine having four conditioning rings, only one or two of the rings are used for containment of parts being lapped. The remaining conditioning rings are not used for machining parts. Instead, they are employed to help condition the table surface and uniformly distribute lapping compound and lubricant on the lapping table. Parts having a generally flat bottom surface that is to be lapped are placed within one or two of the conditioning rings. As the table rotates, the conditioning rings and parts to be lapped each continuously revolve about their own central vertical axes, thus assuring a smooth and uniform lapped finish over the entire bottom surface of each part being lapped.
One long-standing problem presented by the conventional lapping machines designed as just described relates to the loading and unloading of parts being lapped. Lapping cycles vary greatly, depending upon the parts the material they made of, and the quality of the finish desired, from as low as about one minute up to several hours. However, during a typical lapping cycle of five or ten minutes, for example, a significant amount of cycle time is required to start and stop the table, and unload and load of the parts. Traditionally, the individual parts have been removed from the conditioning rings and inserted into the conditioning rings manually. One technique for loading parts is to place them by hand in a circular configuration on a flat board. When the conditioning ring is in an elevated state, the board is then placed under the raised ring in the area normally occupied by a conditioning ring. The ring is then lowered, and the table is started up, so it begins to rotate again. To unload finished parts, the process is reversed.
Recently, automatic loaders for such machines have been provided which shuttle the rings in and out of the table onto flat load/unload surfaces at the same height as the table's lapping surface. Although the table still rotates, the ring containing parts are to be removed from the lapping machine is no longer in productive use when that lapping ring is moved off of the table onto a nearby loading/unloading platform. The net result is a significant loss of productivity when a ring is being loaded or unloaded, even though the table continues to rotate, since no parts are being lapped within that ring for as long as it takes to unload the ring, and load it with new parts.
As part of the conventional lapping processes described above, a large and heavy one-piece weight plate is typically placed over the many parts within an individual conditioning ring. If desired, a piece of cushioning material such as synthetic felt may be placed between the parts and weight plate. In this situation, the tallest parts are necessarily subjected to heavy forced lapping first, since all or most of the weight of the plate bears down on these taller parts. Those parts of lower height are lapped only by the force gravity exerts on the part until the higher parts are lapped down to a uniform height, at which time the weight of the plate begins to bear down on those parts as well. This approach to lapping parts necessarily requires a lapping cycle sufficiently long to ensure that the taller parts are lapped down to the height of the shorter parts, and that the lower-height parts will then receive a minimum desired amount of lapping, as required to obtain the desired surface finish.
In light of the foregoing shortcomings of prior art lapping systems, it is a primary object of the present invention to provide a lapping system and method which allows parts to automatically be loaded onto and automatically removed from a rotating lapping table having a horizontal lapping surface without human intervention. It is a related object of the present invention to provide a lapping apparatus which causes parts to be lapped to move single file in one or more streams across a lapping table, by action of the rotating table rubbing on the parts to be lapped.
It is a further object of the present invention to provide a parts track to guide the parts in a single file across the table. A related object is to provide escapement mechanisms for controlling the timing of movement of the parts between specified locations, which may be called stations, located along the parts track, so as to closely regulate the amount of lapping each part receives. It is another object of the present invention to provide multiple tracks and escapement mechanisms for feeding parts to be lapped in parallel streams across a rotating lapping table.
It is yet another object of the present invention to provide individual powered lapping stations where a positive downwardly-directed force is selectively applied to a part to be lapped to increase the rate of material removal from the lapping table. One more object of the present invention is provide a lapping system capable of efficiently lapping parts of uneven height in a minimum amount of time.